Removing the ascii serializer

Since the string type has two converters (one for utf-8-string, one for ascii-string), the ConverterSelector needs a strategy to decide, which converter should be used to serialize a string.Since the strategy does not exist, it is a first-registered-converts strategy. At least I want to favor utf-8-string and to make it clearly, the ascii-string converter is removed from the serializationConverterList in the default repository. (instead of just reorder the default converter list)